Marketable Securities - Available-for-sale Marketable Securities in Gross Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Available-for-sale marketable securities in a gross unrealized loss position
Estimated fair value, less than 12 months	$ 2,197
Gross unrealized holding losses, less than 12 months	4
Estimated fair value, more than 12 months
Gross unrealized holding losses, more than 12 months
Estimated fair value	2,197
Gross unrealized holding losses	4
Corporate bonds and notes
Available-for-sale marketable securities in a gross unrealized loss position
Estimated fair value, less than 12 months	194
Gross unrealized holding losses, less than 12 months	3
Estimated fair value, more than 12 months
Gross unrealized holding losses, more than 12 months
Estimated fair value	194
Gross unrealized holding losses	3
Municipal bonds
Available-for-sale marketable securities in a gross unrealized loss position
Estimated fair value, less than 12 months	2,003
Gross unrealized holding losses, less than 12 months	1
Estimated fair value, more than 12 months
Gross unrealized holding losses, more than 12 months
Estimated fair value	2,003
Gross unrealized holding losses	$ 1